1. Field of the Invention
The present invention relates to a method for production of semiconductor devices which permits easy removal of native oxide with a minimum damage to the substrate.
2. Description of the Related Art
Plasma treatment has been a common practice in the past technology. It alters the treated layer only slightly with very little adverse effect on reliability and working speed so long as it is performed on the wiring section of large area. However, this does not hold true any longer as the result of recent miniaturization of semiconductor devices, particularly in wiring. Reduced wiring width, increased current density, and multilayer structure require better reliability. An increase in current density is accomplished by employing a conducting film composed mainly of copper which has a low resistance as well as a thin interlayer insulating film with a low dielectric constant. The process for forming an interlayer insulting film on a conducting film composed mainly of copper involves a step of removing native oxide from the conducting film. This step is accomplished by plasma treatment in a reducing gas typified by hydrogen and ammonia. This technique is disclosed in Japanese Patent Laid-Open No. 2003-188254.
Unfortunately, any interlayer insulating film with a low dielectric constant usually suffers from low density and poor mechanical strength. Consequently, plasma treatment with a reducing gas causes the interlayer insulating film to increase in dielectric constant or to recede. On the other hand, chemical treatment without plasma poses a problem with chemical solution remaining on or infiltrating into the insulating film. In order to address these problems, there has recently been proposed a process for annealing in a reducing gas. This process, however, still has many difficulties such as increase in heat amount to be overcome before it is put to practical use.